New GPU performing weirdly

So a few days ago I finally got a new (good) gpu, the Radeon HD 7850. Installing went without any issues, updated the drivers and all (Catalyst 12.8). However its performance is kind of all over the place, but mostly below expectations.
Example : In Deus Ex:Human Revolution the framerate occasionally drops down to 3. Yes, three. While the rest of the game is running at a solid 60 fps thanks to vsync, and in the hundreds with vsync off. It seems to happen in specific areas while looking a certain direction. If I turn around, the framerate goes back up to its normal state.
This might just be something with the way the game is coded, I don't know. So I tried a different game : Saints Row 3. Guess what? It ran at 20-30 fps on medium settings.
In neither of these cases has the gpu OR cpu usage gone above 50%. I know my specs aren't the best, but they should be capable of way more than this.
Specs :
Windows XP 32 bit (Could this be the problem? I don't know... Planning to get Win7 next month regardless)
AMD Phenom II X4 965 BE
4 GB 1333 Mhz RAM (Though only 3(?) GB usable because of 32 bit OS)
Sapphire Radeon HD 7850 1GB
500W OCZ ModXstream.

You might be running into a processor bottleneck here if it isn't overclocked. Your RAM is also a bit low as it's about 3.5GB that a 32-bit OS can use. Try updating the drivers to 12.11, they have significant performance improvements in many games and if it's caused by your GPU it might fix your problem. I'm still suspecting the CPU right here though, did you mean two cores with 100% load with the 50%?

You might be running into a processor bottleneck here if it isn't overclocked. Your RAM is also a bit low as it's about 3.5GB that a 32-bit OS can use. Try updating the drivers to 12.11, they have significant performance improvements in many games and if it's caused by your GPU it might fix your problem. I'm still suspecting the CPU right here though, did you mean two cores with 100% load with the 50%?

There is was a button in Catalyst to update my drivers, and it took me from 12.4 to 12.8, so I guess that might be the 'recommended' driver for me. Will try updating to 12.11 if neccesary.
I've got my pc set to power-save mode, so it automatically downclocks my cpu to fit the situation. While playing all cores were downclocked to 2.2 Ghz (From 3.4 Ghz), I believe 2 cores were at around 50% usage, the other 2 were around 30% usage, so it wasn't maxing out my CPU at all. Catalyst said the GPU activity was around 40%, so also not maxed out.
Might be my RAM then, didn't pay attention to that while playing. Otherwise, any other things you guys know that might cause this problem?

Switch it to balanced, power saver unnecessarily limits the performance(at least on laptops). It will still downclock the processor if it can.
Download the 12.11 from the AMD website if you do update.

Switched the power settings to Home/Office (there was no balanced) It doesnt downclock my processor and it runs a bit hotter now, but my CM 212 EVO can handle it.
As I had excepted, any drivers later than 12.8 don't support windows XP anymore. It automatically redirected me to 12.8 again, though I am reinstalling it because I think I may have made a mistake last time. Reporting back after restarting pc and doing the in-game tests again. Also keeping an eye on RAM usage. Anyway thanks for the help so far

Alright, I did the tests again and there is definetly improvement, though the problem is still not gone. FPS in SR3 is now generally above 30. As for the 3 FPS in some streets/halls in Deus Ex, it has now improved to around 12 fps in those locations. I can deal with that, though it still bugs me. CPU and GPU usage have increased a bit, though it is still not using their full capacity. RAM usage is never more than 2 GB too so that isn't the problem either.
I'm running out of ideas as to what could be causing this. Any ideas?

I'm going to have to go with a defective card, or the card is overheating and underclocking itself.

The max temperature it has reached is 52 degrees celsius, and the clockspeeds don't change at all during gameplay (Readings from Catalysts AMD Overdrive) Unless it is somehow reading incorrect values, this doesn't seem like overheating to me.

The max temperature it has reached is 52 degrees celsius, and the clockspeeds don't change at all during gameplay (Readings from Catalysts AMD Overdrive) Unless it is somehow reading incorrect values, this doesn't seem like overheating to me.

Is there any way to tell for sure, at least give a better indication? Maybe a program like 3D Furmark could help push the GPU to it's full potential? I'm just throwing this out there, because I kind of don't want to go through the process of returning it and perhaps not get a replacement and all that because it has been used already.

Is there any way to tell for sure, at least give a better indication? Maybe a program like 3D Furmark could help push the GPU to it's full potential? I'm just throwing this out there, because I kind of don't want to go through the process of returning it and perhaps not get a replacement and all that because it has been used already.

Try running Futuremark(Candymark) just for the kicks. If you get artifacts or an exceptionally low score on graphics you'll know that it's the card.

Ok I just thought of something (Yes I'm desperate to find a reason behind this). Maybe the 32 bit OS limitation actually picks the RAM over the VRAM of my graphics card. PCMark05 just told me I have 3.3GB of RAM, so IF RAM and VRAM have to share the 3.5ish GB that a 32 bit OS has, it takes 3.3GB RAM and barely any VRAM. It would explain why only some areas are laggy : too many objects to fit into the VRAM. Just a theory, but sounds plausible, right?

Try running Futuremark(Candymark) just for the kicks. If you get artifacts or an exceptionally low score on graphics you'll know that it's the card.

I couldn't find the one you are talking about, but Futuremark.com showed 3DMark, PCMark and PowerMark. Only PCMark has a version that works on Windows XP, but it doesn't allow for the testing of individual components (At least, the free version of it doesnt). Could you give a link to the one you are talking about?

These kind of problems are always a bit hard to solve because it can be so many things.

I can without a doubt say that your system should be running DE:HR easily. My Phenom II x4 B55 @3,6Ghz and slightly overclocked 6850 could run it without any problems. So it's not any bottleneck.

Have you overclocked your cpu?

Are you sure you have plugged in the extra power connector to the new graphics card?

What are the max temps of your cpu and gpu while playing/under load?

Yeah, my pc runs DE:HR just fine for the most part, but some areas (Mostly in the city, so wide open area) make the framerate drop hard. Then in different parts of the same city the framerate is in the hundreds again. So weird.
I have nothing overclocked in my system, and I do have the extra pci-e connector plugged in.
Max GPU temperature I've seen while playing was 52 degrees celsius. Max CPU temperature around 46 degrees, give or take.
I really want to blame WinXP 32 bit for this, but by the time I have the money for Win7, I think I might be too late to return the GPU (should it be faulty after all) so I'm still trying to figure out what to do here.
Will be trying some more different GPU intensive games tomorrow to see if the results there come closer to the benchmarks.

Yeah, my pc runs DE:HR just fine for the most part, but some areas (Mostly in the city, so wide open area) make the framerate drop hard. Then in different parts of the same city the framerate is in the hundreds again. So weird.
I have nothing overclocked in my system, and I do have the extra pci-e connector plugged in.
Max GPU temperature I've seen while playing was 52 degrees celsius. Max CPU temperature around 46 degrees, give or take.
I really want to blame WinXP 32 bit for this, but by the time I have the money for Win7, I think I might be too late to return the GPU (should it be faulty after all) so I'm still trying to figure out what to do here.
Will be trying some more different GPU intensive games tomorrow to see if the results there come closer to the benchmarks.

If the gpu is broken it will go to the warranty, don't worry about that. And if the gpu would be broken there would be artifacts etc. so I wouldn't say it's that.

Do you have that ram in 2x2gb sticks? If yes, try taking one of the sticks off and test playing it. This will allow the computer use the whole 1Gb vram of the gpu. If the performance is even slightly better then you'll know what's causing it all, the 32 bit OS.

Normally I would agree, but I've been seeing a lot of cards (since the 7000/600 series started) with this exact same issue that are defective, with no artifacts or anything else at all, just poor performance as the only symptom.

Something tells me it is a manufacturing problem with how some of the new cards are laid out on the PCB but I don't know enough about all of that to say definitively one way or the other.